Proper function of the brain requires that neurons adopt different morphologies and connections. Specific gene regulation is likely to mediate these events. In the nematode C. elegans, mutations in the UNC-4 homeodomain transcription factor miswire the motor neuron circuit and disrupt movement. UNC-4 and the Groucho-like cofactor UNC-37 function together in the affected motor neurons to repress target genes, a subset of which controls synaptic specificity. The goal of this project is to identify these genes. The promoters of two known UNC-4 targets (acr-5 and del-1), which do not regulate synaptic choice, will be analyzed to define UNC-4 Response Elements (U4RE) that mediate repression. Upstream regions will be deleted to identify sequence motifs that are required for unc-4 regulation. Identified U4REs will be used in gel shift experiments to determine if UNC-4 binds directly to these sites, which should also be present in other unc-4 regulated genes. Since UNC-4 and UNC-37 function as repressors, targets genes should be elevated in unc-4 and unc-37 mutants (compared to wildtype). The full genome C. elegans microarray will be probed to detect these differentially expressed genes. The promoters of candidate targets will be scanned for U4REs. Genetic methods will be used to test authentic UNC-4 targets for their roles in the synaptic specificity pathway that UNC-4 regulates.